Although a broadband is required for faster communications, it is difficult to reserve a common broad frequency band available around the world due to a variety of operating radio communication systems. For this reason, there is being discussed an approach for using several frequency bands to assign priority of frequency utilization to each of the frequency bands and allowing several radio communication systems to utilize a common frequency band. Also, since it is hard to reserve such a common frequency band available around the world, a terminal apparatus must selectively use frequency bands among several frequency band candidates in different countries, and accordingly some components are needed for identifying radio communication systems presently operated in the terminal apparatus residing area depending on areas where the terminal apparatus is used. However, a large amount of consumed power and/or a long identification time period are required for the terminal apparatus to identify available radio bands from a very broad band where many radio communication systems may be operated. Also, in environments of shared frequencies, a higher priority assigned radio communication system (referred to as a primary system hereinafter) and a lower priority assigned radio communication system (referred to as a subsidiary system hereinafter) use the same frequency band for communication while avoiding interference to the primary system. This technique includes some techniques for calculating the amount of interference to the primary system based on propagation loss between the primary system and the subsidiary system and some techniques for controlling transmit power of the subsidiary system depending on the calculated amount of interference. In addition, in consideration of the traffic amount during communication by the primary system, an allowable amount of interference may be determined, and the transmit power of the subsidiary system may be controlled. For example, the allowable amount of interference may be set to be larger in a time period of a less traffic amount in the primary system, and the subsidiary system can be controlled to operate at a higher level of maximum transmit power than a time period of a larger traffic amount in the primary system.
In the case where this type of technique is used, frequency utilization schemes are dynamically changed, and thus a terminal apparatus must always utilize functions of identifying available frequency bands and radio communication systems.
A cognitive pilot channel (CPC) for broadcasting information items such as frequency bands and radio schemes available in individual radio communication systems operated in each area is proposed to handle the above-mentioned dynamic change in the frequency utilization schemes. Applying the CPC enables the terminal apparatus to do without scanning fundamental parameter information on connectable radio communication systems. Also, in the case where the CPC is applied, some parameters of the radio communication systems can be changed by changing the above-mentioned control information. In addition, the CPC can be applied without modification of the terminal apparatus itself.
Thus, this technique can decrease cost of the terminal apparatus and address change in the parameters for the radio communication systems, which can improve the frequency utilization efficiency.
In the technique, a coverage area of a base station apparatus is divided into multiple areas. The divided areas may be referred to as meshes. In the areas covered by the base station apparatus, a control signal is broadcast. Also, the base station apparatus indicates a utilization scheme of radio resources such as the fundamental parameter information of the radio communication systems for each mesh several times. The same information may be broadcast. Also, there are two types of control signal delivery methods, that is, a broadcast type delivery method and an on-demand type delivery method. In the broadcast type delivery method, a base station apparatus periodically broadcasts control information corresponding to meshes within its coverage area. In the on-demand type delivery method, in response to a delivery request from a terminal apparatus, a base station apparatus delivers control information corresponding to a mesh where the requesting terminal apparatus resides. Also, a hierarchical advertiser CPC has been proposed. In the hierarchical advertiser CPC, several delivery stations and means are utilized, and a delivered control signal is partially separated.